How to add an extra row of 1's at top of a NumPy array [duplicate]

Question

An array is present as:

a[[12,31,5], [5,32,1]]

I wish to add a row of 1's such that it becomes:

a[[1,1,1], [12,31,5], [5,32,1]]

How to do it?

Sergey Bushmanov · Accepted Answer · 2019-01-31 16:29:40Z

0

All you need is np.vstack:

a= np.array([[12,31,5], [5,32,1]])
np.vstack([np.ones(a.shape[1]),a])

array([[ 1.,  1.,  1.],
       [12., 31.,  5.],
       [ 5., 32.,  1.]])

A slightly more involved is np.r_:

np.r_[np.ones(a.shape[1]).reshape((1,-1)),a]
array([[ 1.,  1.,  1.],
       [12., 31.,  5.],
       [ 5., 32.,  1.]])

answered Jan 31, 2019 at 16:05

Sergey Bushmanov

25.5k8 gold badges63 silver badges84 bronze badges

Sign up to request clarification or add additional context in comments.

1 Answer 1